The invention relates to an apparatus for controlling a double-acting working cylinder having a piston with one-sided piston rod by means of a multiway valve, which supplies the working medium to one of the differently sized swept volumes of the working cylinder, respectively, and permits it to flow out of the other swept volume during the piston stroke. The multiway valve, which is designed in the manner of a piston valve, has a pump connection P, a connection A1 for an inflow and outflow line between the large swept volume of the working cylinder and the multiway valve, a connection B1 for an inflow and outflow line between the small swept volume of the working cylinder and the multiway valve, a connection A2 for a connecting line connected to the inflow and outflow line positioned between connection A1 and the large swept volume of the working cylinder, and two reservoir connections T1, T2. The valve piston of the multiway valve has at least five control edges disposed on ring collars and the connections P, A1, A2, B1, T1, T2 are disposed in such a way that as the piston is extended, to use the differential action of the working cylinder with rapid piston motion, connection B1 is connectable with connection A2 and, as the piston is retracted, connection A1 is connectable with T1 and connection A2 with T2, whereby at the end of the differential motion with extended piston rod of the working cylinder, connection B1 is connectable to a line leading to the reservoir to build up force.
DE 30 00 260 C2 describes an apparatus with the aforementioned characteristics. The circuit arrangement disclosed therein, which assigns six connections in series of the multiway valve employed, is intended on the one hand to permit travel of the working cylinder piston with differential action, i.e., with rapid piston stroke, and on the other hand to ensure as compact a structural design of the multiway valve as possible with uniform pressurization of the five control edges provided on the multiway valve with the same quantity of working medium in both travel directions of the piston of the working cylinder.
For this purpose, in the known apparatus, as the working cylinder piston is extended, the additional connection opening connected to the large swept volume of the working cylinder via the connecting line, is connected with the line acting as the outflow from the small swept volume via an associated control edge, which controls only the flow of working medium passing through this connecting line. At the same time, via another control edge and thus independently from the flow path between the swept volumes of the working cylinder, the pump connection is connected to the inlet of the large swept volume of the working cylinder. At the same time, as the piston of the working cylinder is retracted, the connection with the reservoir can be established through an additional connection provided in the multiway valve.
To effect the forward motion of the working cylinder piston utilizing the differential action of the cylinder while using the full force in the extended end position of the piston rod, a directional control valve with two switch positions is additionally placed in the connecting line. When the piston rod is in its extended position, the directional control valve switches to a position where the connection between the small swept volume and the large swept volume, which is provided by the interconnection of connections B1, A1, is interrupted and the small swept volume of the working cylinder is connected to the reservoir. In this position of the directional control valve, the pressure acting on the large area of the piston of the working cylinder is no longer counteracted by a pressure in the small swept volume of the working cylinder such that the holding force is doubled compared to the state existing during extension of the piston rod.
The disadvantage of this known embodiment is that the additional directional control valve adds complexity to the corresponding design of the control apparatus. This is particularly true because the directional control valve must be designed for the same rated quantity as the multiway valve, which serves as the main control of the working cylinder, since the addressed functional case of connecting the small swept volume with the reservoir requires the same flow of working medium to be directed through the directional control valve as through the multiway valve.